Igniting device for liquid fuel burners



2 Sheets-Sheet l M. A. POWERS IGNITING DEVICE FOR LIQUID FUEL BURNEIRSFiled June 20,

May 3,1938.

s 3v P May 3, 1938. r M. A. POWERS 2,115,373

IGNiTING DEVICE FOR LIQUID FUEL BURNERS Filed June 20, 1954ZSheets-Sheet 2 BY MW ATTORN 5 past May3,1938 7 T g 2,115,873

UNITED STATES PATENT-OFFICE ,rom'rmo mtvi i lit LIQUID FUEL BURNEBBMilton s. Powers, Detroit, Mich, assignor; by

mesne assignments, to The 'llmken-Detrolt Axle Company, a corporation ofOhio Application June 20, 1934, Serial No; 731,562

14 Claims. (01. 175-115) The present invention relates to devices forvoltage and minimizing r'adio interference. Lo-

igniting liquid fuel burners',-and it is more parcating the arc in azonethat is protected from ticularly concerned with igniting devices foroil the high velocity air currents also permits the burners of thegeneral character employed for arc to heat the surrounding air andvolatilized oil heating residences, although it is not limited to to ahigh temperature, resulting in rapid vaporius th t s type of burner,zation and ignition of the combustible mixture;

In some types of oil burners, ignition is easily The present inventionpossesses all 01' the highly possible, as there is some point in thecombusmportant features of the construction disclosed tion zone where areadily ignitable mixture may in y P Patent 1 5' fi d. (T8180 P 10always be found and in which an electric spark sesses several furtherhighly desirable character 10 gap may be located. However, in a liquidfuel istics that will hereinafter appear. burner o! thewall flame type,for instance, a Certain features of my invention are disclosed verticalrotary burner, where combustion takes in my c pc s ppl cation, SerialNumber place at a distance from the source of air and flied June 12,1933, and the present apm gupply, t eondmondoes t xi t, In h plicationis accordingly a continuation in part of 011 burners the oil isordinarily thrown in a subsaid co-Pend ng application. stantially solidor tin-atomized state toward a t s a p m y j t f th pr sent inventionrefractory combustion surface, where it is broken to devise a novel liquel burner of the wall up and voiatilized,inixed with air and combusted.flame p a g an ignitin d ce which is so In burners of this type, theconventional electric lwsiiiive in P -i and ye which is simp e sparkwill i'requently ignite the air iuel mixture in desis'hv m in the regionof the combustion surface, when It further i jec f y vcntion' c thelatter is hot, but this is almost impossible vi e an improved burnerorganiz ion h n a of achievement when the combustion chamber carburetingwall of low heat content and an ignit- 0 has been completely cooled.Moreover, in such s device oca ed a j e 80 h when u devices, the sparkbetween the electrodes is excombustion is initiated the carbureting wallwill tendedor drawn out by' reason 01 the high ve- 1 li quickly and p dy vo atilize fuel imlocity air striking it, and eventhough a very hot pn in t r asains and pr pa ation of comspark may be used, the heatthereof is not conbustion will be "D served, but is dissipated into therapidly moving It is another impor n bi f my nv ntion air streamsurrounding it. Accordingly, in such to P ovide an i p burner ati navdevices, the oil spray passes between or near the B ur t ns W d posedsubstantially eleetrode, and while at times it may be momennormal to thedirection of fuel directed there- .tarily ignited, the high velocity orthe surroundains with a member inclined to t earbureting air preventsthe flame from propagating and 8 wall for deflectihs air upwa d y ver1128 lil ignition iallure results. i face, and withmeans, locatedbetween the de- In my prior patent, No. 1,888,695, granted .Nofleet nmember and e ca bu et ns wall. for vember 22, 1933, I have disclosed anigniting is i ns l P B E gainst the latter. device for an oil burner 01'the general character It is B ep le t 0 y ven ion to devise 40 Justdiscussed, and it has proven satisfactory for h improved having ametallic carburet- 40 such burners, for the reason that electrical en- 1ingwall and several el rod s loc te jacent any, with. a secondary m oftwenty-five thereto, the carbureting wall forming ag'partoimilleamperes, is supplied the electrodes through the c t between theelectrodes.

a transformer having an input of at least seventy- A further j of yvention is to devise flve watts, with the result that a flaming arc, asan m v d tal i ar t n's element havi s distinguished from a Jump sparkor intermittent a non-metallic electrode associated therewith for sparkis produced. Moreover, in my prior con- 8101118 cooperation with 880mmelectrode which struction the flaming arc is sheltered from the isinsulated irom the carburetin'g element. high velocity air stream, or islocated in a semi"- y ntion further aims to P de metallic 5o quiescentzone, whereby the air and volatilized oil l q d iu i r retins elementwith a built in" in the region 0! the arc moves comparatively orembeddedelectrode, which s v es g ed that slowly into the combustion zone, withthe result it does not change the configuration oi the surthat thehydro-carbon and air ionize to a great face 01. the carb'iiretingelement. extent and accordingly greatly reduces the gap It is anotherobject of my invention to deresistance eflecting a substantial loweringof the vise novel means for mounting an ignition e1ec-; 55

trode in senibly.

A further object of my invention resides in the provision of .a liquidfuel burner of the character having a hearth and means for burning fuelabove the hearth, with an improved electrode having nested members thatare joined together below the hearth, whereby the joint is protected.from the direct heat of the burning fuel.

.It is another object to devise an electrode for use in a liquid fuelburner, which is so constructed that the parts thereof may freelyundergo expansion and'contraction in response to thermai. changes,whereby distortion or fracture thereof is avoided.

It is another object to devise an electrode for use in a liquid fuelburner having parts that may freely move relatively in response totemperature changes, and yet which are positively restrained Zgainstimproper movement in response to vibraons.

Further objects of my invention will become apparent as thespecification proceeds in connection with the accompanying drawings, andfrom the appended claims.

In the drawings: a

Figure l is a vertical sectional view of a coalburning furnace, havingmy liquid fuel burner and igniting devices applied thereto.

Figure 2 is a perspective view of one of the igniter assemblies employedin the device shown the hearth of a liquid fuel burner asin Figure 1, asit appears when removed from the furnace.

Figure 3 is a sectional view taken on the line 3-3 of Figure 1, lookingin the direction of the arrows.

Figure 4 is an enlarged vertical sectional view of the lower part of oneof the electrodes employed in the device shown in Figure l.

Figure 5 is a diagrammatic view of the transformer and the circuitemployed for connecting it to the carbureting ring of the constructionillustrated in Figure l.

Figure 6 is a diagrammatic view showing a modified form oftransformer'for use with my burner and igniter construction. w

Figure 7 is a fragmental sectional view of a modified form of electrode,also forming part of my invention.

' Figured is a vertical sectional view of liquid fuel igniter and burnerembodying my invention, but illustrating it mounted in a hearthconstruction of modified form, and

Figure 9 is a fragmental sectional view of one of the electrodesemployed in the construction shown in Figure 8 and the associatedstructure.

With continued reference to the drawings, wherein like referencecharacters have been employed to designate like parts throughout theseveral figures thereof, my liquid fuel igniter and burner is shown inthe present instance as being mounted in a furnace A, and it consists ofa hearth assembly B, supported in the furnace, .a burner head C,whichthrows oil and air outwardly .toward a fuel volatflizing and combustingassembly, consisting of cooperating segments D which form a carburetingring. A plurality of igniting devices E cooperate with the carburetingring to ignite the fuel-air mixture and electrlc energy is suppliedthereto from a transformer F, which is preferably grounded to the burnerhead assembly, as at G. Control of the device is effected by mechanismlocated In a. control stand H, and as the latter forms no part of thepresent invention, it will not be further described.

auaevs The furnace or boiler base is provided with an inwardly extendingflange I l upon which the outer edge of a hearth supporting plate l2rests, and the inner periphery of the latter is supported on the outerportions of split rings l3, which are supported in a grooveprovided inthe burner head. The hearth proper consists of a refractory material,indicated at M, which is molded upon the hearth supporting plates. The-"just described, and the means utilized for controlling oil and airfiowforms no part of the present invention as it is claimed elsewhereand is, fully considered, for example, in my Patent No. 2,051,130, ofAugust 18, 1936, which may be referred to for a more detailed disclosureof these parts. I

Immediatelyabove and resting upon the hearth is a series of metallicsegments 22, which are firm- 1y clamped together in any suitable manner,so as to form a continuous ring, that is spaced inwardly from the boilerwall. Each segment. is

provided with a groove gutter portion 23, a vertical flange 24 or impactwall and an upwardly sloping, air-deflecting portion 25. All of thesegments except the igniter segments are identical in construction andhence they are interchangeable. -The detailed construction of theigniter. segments will be described hereinafter.

A. plurality of grills, designated generally as 25; are supported attheir inner ends on portions 2t of members 22, and at their rear endsupon members 2I, which in the present instance are also utilized tosecure the various segments in assembled relationship. Segments 22 andgrills 26 and connectors 21 are all preferably constructed of a. specialheat-resistant steel in order to withstand the high temperatures towhich these parts are subjected when the burner is in use.

Grills 2S function to hold the flame down where it. may be moreadvantageously utilized, and as they are fully disclosed and claimed inthe application of John A. Wilson, Serial No.

682,374, filed July .27, 1933, which may be referred to for a morecomplete disclosure, they will not be further described in the presentapplication.

With respect to Figures 1 and 2, two diamet rically opposite segments 22are each provided withan igniter assembly, and the electrode thereof'that isbuilt in. or embedded in the carbureting ring, will now bedescribed. Each ring electrode consists of a. preferably metalliccontainer 28, whose side. walls are shapedto conform to the shape ofgutter portion 23 01 segment 22, and are welded to segment 22 as at 29.Each container orbox 28, is filled with a carborundum mass 3|, which ispreferably formed by mixing granular carborundum and an insulatingrefractory binder and water, to form a plastic mass, which hardens to a.solid mass presenting a face which is curved to conform substantiallyexactly with the curved surface of gutter portion 23. As seen in Figure3, .an aperture 32 is formed in segment 22 through which mass 3|extends, so as an s-rs to render a portion of the interior of the ring acurved electrode surface. The insulating material is incorporated withthe carborundum in order to increase the resistance thereof and therebycause it to heat up when a current is passed through it.

Although I prefer to equip the carbureting ring segment with separate orindependent elec- 'trodes, it is to be understood that in some cases,

particularly if high quality fuel is.used, it may be desirable toeliminate pocket 28 and its carborundum insert, thus allowing theinner-electrodes s to fire across the gap directly against the metalsurface of the ring, and it is to be understood that the appended claimsare intended to cover my device when it is used in this manner.

Cooperating with each ring electrode is an inner electrode that will nowbe described. An-

outer insulating member 35 having apair of nibs 36 formed at its upperend, and having an apertured bottom 31, extends through an aperture inplate l2 and is embedded in hearth l4. Member 35 is frictionally held ina clamping member 8) by means of a screw 39, and the clamp is providedwith an upwardly extending portion that is secured to a pressed verticalcylindrical portion ll of member 22 by a welding operation, indicated at42, or the like. As previously indlcated, members 35 are embedded inhearth ll, along with clamp member 38, when the hearth is molded inplace upon the hearth plates.

Extending through the apertured bottom of each member 35 is an innersleeve-like insulating member 43; which is rigidly secured thereto bycement or any other suitable means. "Sillimanite" is the preferredmaterial from which insulator elements I! and l! are made, for it hasbeen found that its insulating abilities remain intact at highertemperatures than other known insulating materials that are practicalfor use. A conductor 44 extends rather loosely through inner insulatorl3 and is formed with a pair of nibs or ears 5 at the upper end thereofwhich rest upon a washer 48. Bars 45 cooperate with washer 46 andaccordingly restrain conductor ll against downward movement under theinfluence of gravity. Secured to thetop of each conductor II, as by awelding or riveting operation, is an electrode 41 which ispreferablymade of a heat resisting metal, as is also conductor H. and has a lug atits inner end into which conductor H ex-' tends. As seen in Figures 1and 2. e ectrode 41 isof ribbonlike construction and has an unwardlycurving portion that extends from the lug "to itemain body portion andthen slopes slightly downwardly toward its outer end where it termin,ina somewhat blunt tin II. V

. As seen in Figure 1, each tip 0 term nates a short distance away fromthe carborundum ring electrode thus ,forminga spark or-arc gap. The tipportion of each member 4,! is shaped so that the arc will pass suddenlybetween two points if .there is no outside influence. However.

upon movement of the surroundin atmos here.

. each electrode 41 is provided with a lateral downwardly deflectedextension I and it is disposed on the side toward the air spray. A notchBI is formed at the junction of the outer edge of the downwardly'deflected extension and the main body of the electrode.

As previously stated, conductors ll are only loosely disposed withininner insulating members 43, and this is done in order to allow thesememhers to freely expand and contract both longitudinally and radiallyunder the influence of temperature changes without causing fracture of rthe insulator. In the electrodes heretofore proposed, wherein theconductor was closely disposed within inner insulator, it was found thatupon gradual heating of the parts the metal would expand faster than theinsulator in view of its greater coetiicient' of thermal expansion, withthe result that the latter would often be fractured. On .the other hand,conditions are sometimes encountered wherein the porcelain expands morerapidly than the metal. For example, upon rapid heating in a coldboiler, that portion of the insulator surrounding the electrode may besubjected momentarily to a much greater temperature rise than theconductor, with the result that despite the lower coefficient ofexpansion of the insulator, the parts of such prior electrodes becomeloose under such conditions and allow the electrode tip to rock out ofproper gapsforming relationship. I have overcome all of these dimcultiesby loosely mounting the conductors within the inner insulators, and byproviding means for positively holding the conductors in'flxedrelationship to the carbureting ring, so as to maintain the electrodesin proper angular position at all times. The structureI preferablyemploy for producing these results will now be described.

With particular reference to Figure 4, the lower end of each conductorll is provided with a flange or boss 52, which is preferably spaced fromshaped spring-steel clip member 54. The fingers of each clip member 54frictionally engage a pair of flat faces 55 provided on insulator l3 andthereby prevent conductor 44 from rocking within insulator l3, and asthe latter is rigidly secured to insulator 35, it is obvious that eachelectrode I1 is positively maintained'in proper gapforming relation w thelectrode 3| at all times.

It should be particularly observed that the points oi connection betweenthe insulators 43 and clips 54, and the joint between insulators 5B and43 are located in a regionthat is below the hearth and they aretherefore not exposed to the direct action of the flame.

.It is observedthat the upper end of each conductor 44 extends above theplane of insulators 3i and II. This is done fortwo reasons: first, thereis less area disposed for deflecting the air issu ng from burner head 0.and second. the expansion and contraction of conductor is a maximum inthis region as it is exposed to the radiant heat developed above thegrills.

Electrical energy may be supplied to the electrodes in any suitablemanner, but I preferably employ a transformer having an input of approxmate y '15 watts and a secondary current of Referring now to Figure .5,p

.by wires i'l. with the igniters which in these figures are indicated byarrows E. The secondary igniting point of view, without grounding themidpoint of the secondary circuit, or the carorder to minimize radiointerference. It is accordingly desirable to eifect a good electricalconnection between the various carbureting ring segments, and alsobetween the latter and the boiler in order to prevent any sporadicsparking which might otherwise occur and manifest itself as radiointerference.

It is becoming common practice for the manufacturer of rotary wall flameburners to use a motor equipped with a condenser as a substitute for theusual starting winding and switch mechanism of the conventional splitphase motor, and I have indicated such condenser at 62 in Figure 5, asbeing connected across the power wires 63. The condenser remains in thecircuit during the entire period of operation of the burner, and inaddition to functioning as a starting device for the I motor, it servesto greatly reduce the oscillat- "ing currents, set up-in the secondarywinding when the ignition system is operating, from feeding back intothe power wires and thence into radios where they would manifestthemselves as audible disturbances. The condenser has the capacitance of3m. f. d., and has been found to greatly reduce radio interference inmany cases where trouble has been experienced.

When ignition of the fuel has been successfully inaugurated, the currentfor the primary circuit of the transformer is automatically broken bymeans of a device indicated at 64, which is disposed adjacentthe'combustion zone and is re: sponsive to temperature changes. In viewof the fact that this mechanism forms no part of the present inventionit will not be further discussed.

The operation of my device will now be described and it will be assumedfirst that the carbureting ring is substantially cold. I

When the motor circuit is closed under such conditions, the transformersets up an initial potential diilerence across each electrode ofapproxi. mately 7500 volts. That is, a total voltage drop of 15,000volts across both gaps. However, arcs are immediately establishedbetween the points 48 of electrodes 41 and the curved surfaces ofelectrodes 3 I which is of a flaming character, that is, it is not anintermittent or puncturing type of discharge. The flaming arcs producedby the electrodes rapidly ionize the air and hydrocarbon vapors in theregions of them, and the resultant decrease in the resistance of thespark gaps materially reduces the voltage drop, and this accordinglyresults in a tremendous reduction of the strain in the high voltagecircuit and minimizes tion of the outwardly and upwardly moving aircurrents emanating from the burner head, with the result that they arenot drawn out, and the air and hydrocarbon vapors in the region of thethe gutter that are remote from the igniters.

' trodes has been effected, and it is to be particularly hearth are notdisplaced, with the rwult that the heat of the arcs is conserved, andthe temperature of the hydrocarbon vapors raised greatly. Under theseconditions the arcs maintain a bushy white appearance, as distinguishedfrom the reddish appearance they exhibit when operated in the open air.

In view of the fact that gutter 23 is substantially protected againstair movements, the main flow of air moves upwardly past the carburetin'gring without entering the gutter, where it is mixed with the oil vaporsarising from the gutter. Accordingly, the mixture in the gutter, exceptin the region of the ignitors, is too rich for combustion. However,downwardly. curving portions 49 formed on electrodes 41 cause a portionof the upwardly movingmain body of air to be directed downwardly intothe gutter and adjacent the arcs. The air supplied the arcs in thismanner not only exerts a scouring action and hence keeps the electrodesclean, but it also supplies sumcient oxygen for the inauguration ofcombustion of the hydrocarbon-air mixture adjacent the arc, and fromthese two points flame propagation extends circularly in both directionsaround the carbureting ring, and upwardly thereof, in view of the lackof a combustible mixture in the portions of It is not only important toproperly inaugurate combustion, but it is absolutely essential toemciently propagate combustion after ignitionof the hydrocarbon mixturein the region of the elecobservedthat even though the carbureting ringis constructed of metal, which has a comparatively high specific heat,it is thin and accordingly has a low heat content and heats up rapidly,with the result that it rapidly volatilizes the substantially liquidfuel impinging thereon from head l5, and fuel volatilization isaccordingly very emcient.

An added advantage resulting from the introduction of air to thevicinity of the arcs exists when the burner is called upon to start withthe hearth ring in a highly heated condition. Under these circumstancessubstantially all of the oil discharged from the burner head isimmediately vaporized upon impingement against the carbureting ring. Thelarge volume of vapors immediately fills the gutter in which the arcsare located, and as the vapor in the tube is too rich for combustion,ignition would lag unless air was introduced to the arcs, as provided bymy device.

Soon after ignition has been effected, any excess oil that may bepresent in gutter 23 is vaporized and when the vapor release becomessumciently high, either from oil accumulated in gutter 23, or from oilstriking impact surface, the flame entirely leaves the gutter and burnsabove grills 26.

The amount of air introduced into the region of the arcs may be variablyadjusted by properly twisting downwardly extending portions 49 ofelectrodes 41 to interpose a more or less extended surface in the airpath immediately adjacent the arcing gaps. The air directed to thevicinity of a the arcs also serves to burn away any carbon which mighttend to collect between the electrodes from any cause,among which mostimportant are the incomplete combustion of poor grades of oil, crackingof oil under the intense heat of the arc, or the action of stringycarbon structures which have been found to bridge the electrodes inprior constructions when starting cold.

The substantially flat nature of each electrode 3|, when taken inconnection with the blunt formed on burner C.

employed with my burner igniting devices, they nature of tip 48 ofelectrode 41, and the air currents directed thereto by portions 49 ofelectrodes 41, causes the arc to .wander over a portion of electrode 3|.Such wandering of the point of arc impingement eliminates any badeffects that have been manifested in prior constructions, due to a slowbuilding up of a pile of carbon between the electrodes. metal and iscomparatively thin, it heats up more rapidly and attains a highertemperature than the 5 old ceramic tile, with the result that no troubleis Washer 460 is provided with a downwardly extending flange or lip 61,which is spaced from the cylindrical wall of insulator 43 so that thetwo parts may readily independently expand and contract radially inresponse to temperature changes. Washers 46a are designed in this mannerso as to prevent oil from finding its way between conductors 44 andinsulators 43, as it might leak downwardly and gum up the terminals.Accordingly oil trickling down the conductor 44 is deflected into theannular cup between insulators I5 and", where it is volatilized andburnt when the burner attains a sufllcient temperature.

With reference to Figures 8 and 9, I have illustrated my invention asapplied to a burner having a metallic hearth construction. In this formof the invention an annular plate is secured to flange Ila of boiler Aby means of nuts and bolts and it rests at its inner edge upon a flange69 r A layer of heat insulating material II is disposed immediately ontop of plate '8 and serves to shield the latter and motor I. from thehigh temperatures developed in the furnace. Resting 'on top of insulatorII, and removably secured to plate 88 in any suitable manner are aseries of i i-shaped hearth supporting members 12, which are disposed atintervals radially around the burner head and the upper portion of whoselegs are bent to support a metal hearth ll. Hearth I3 is apertured andlipped at its inner diameter to fit snugly on a shoulder provided onburner C, and has a deep lip 14 at its outer periphery so as to define afuel catching pan. The construction just described is also shown in myapplication Serial No. 129,928 filed on June 9, 1934 now Patent No.2,065,393.

The igniter assemblies extend through apertures in members 88 and II andthrough upwardly flanged apertures .15 in hearth plate 13. Insulators 35are held in proper assembled relation with the hearth assembly by meansof clamps 18 which are preferably welded to the bottom face of plate 68as at 11. Clamp ii is held in position by means of a screw I8, whichextends through the meeting ends thereof. this form of the invention,carbureting ring segments 22 are provided with flanges 19, which arepreferably welded to hearth plate 13 at spaced points, as at 80, whichresults in an extremely rigid construction.

With further reference As the carbureting ring -is made of may be of anysuitable form, but 1 preferably use a transformer designed to deliver asecondary circuit-power of relatively low power factor, and whose waveform is flattened and has a step wave front so that the wave passesthrough zero rapidly. This minimizes the length of the intervals of timebetween each cycle when no current is flowing with the result that theare produced is of a flaming character, andis not extinguished eachcycle. This type of secondarycircuit power wave may be produced in anysuitable manner but I preferably bring it about by incorporatingmagneticshunts in the magnetic circuit of the transformer, and as transformersof this general character are well known in the electrical art, and as Imake no claim to it aside from in combination with the igniter of aliquid fuel burner, it is believed unnecessaryair deflecting means beassociated with the hearth or carbureting ring for directing air to thearcs, or, if the'carbureting ring is designed to produce properair-vapor condition at the arcs, the air deflecting means may be omittedaltogether without departing from the spirit of my invention.

The invention may be embodied in other spe- 'cific forms withoutdeparting from the spirit or essential characteristics thereof.embodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention being,indicated by the appended claims rather than by the foregoingdescription, and all changes which come within The present I the meaningand range of equivalency of the claims are therefore intended to beembraced therein. 7 What is claimed and desired to be secured by UnitedStates Letters Patent is:--

1. In a liquid fuel igniting and burning apparatus, a metalliccarbureting element: means for projecting fuel toward said carburetingelement;

means for igniting said fuel, comprising at least two electrodes spacedstationarily disposed in proximity to definite spaced portions of. each"other and from said carbureting element; and means for establishingelectric arcs between said electrodes and-said definite] spacedportions. of

said carbureting'element, sai d carbureting element forming between saiddefinite spaced portions a part of theci'rcuit for said last-named 3.Inja liquid fuel burning apparatus in .sub-

combination, a metallic element against which fuel is adapted to besprayed; said element haviiian aperture therein; and an electrode: ofhigher resistance than said element mounted on said element inelectrical contact therewith and iii-registry with said .ap erture. 4.{1Ehe apparatus described in claim 3, wherein said e'lement has integralmetallic supporting meansiand said electrode comprises a carborun dumbody having refractory insulating material disseminated therethrough andcarried by said supporting means.

5. In a liquid iuel apparatusin subcombination,

an aperturedhearth having an upper surface whichis subjected to the heatof the burning fuel; an electrode for igniting said fuel extendingthrough said electrode comprising inner and outer concentric insulatingmembers and means, located below the upper suriace of said hearth,

for holding said outer member in position in and against verticaldisplacement with respect to said 8. The apparatus described in claim 7,wherein said means is operable to allow said conductor and insulator toautomatically undergo relative longitudinal movement in response totemperature variations.

9. The combination with a combustion chamber having a metal combustionring, of an elec- .trical ignition system having two pairs oielectrodes, one electrode oi. each pair being electrically insulatedfrom said ring and the other being electrically connected therewith andthe insulated electrodes being connected to opposite sides of a commonsource of electricity, whereby said ring serves as a part oi theeIectriecircuit for the two pairs of electrodes.

10. An ignition system for oil burners having a hearth and metallicflame ring consisting of a source oi electrical energy, electrodessupported by the hearth and projecting therethrough, second electrodesattached to and-embedded in the metal flame ring adjacent the firstmentioned electrodes thereby forming a spark gap therebetween, saidelectrodes being connected in series with said metal flame ring.

11. An oil burner equippedr with a metal flame ring, a hearth, andelectrical ignition means wherein at least a portion of said metal flamering forms a part of the electrical circuit, said electrical ignitionmeans comprising electrodes projecting through said hearth andcomplementary electrodes therebetween embedded in said metal flame ringadjacent said projecting electrodes to form spark gapswith respectthereto.

12. In a liquid fuel burning apparatus, an ignition'system including awall of thin metal of high heat resistance'and of good electricalconductivity, an electrode comprising a block of material of higherelectrical resistance than said' wall, thin metal supporting meansintegral with said wall to position said block of material, and

a second electrode disposed adjacent said block to form therewith aspark gap.

18. In the apparatus deiined in clair'n 12, said wall having a portioncurved to form a concave fuel impingement face, said curved portionhaving an aperture, said block fitting said aperture and extendingtherebeyond in a direction to the rear of said lace, and said metalsupporting 1 means likewise projecting rearwardly from the edge of saidaperture.

14. In a liquid fuel burning apparatus, anelongated iuel impingementmetal ring carrying a pair of spaced electrodes and itself establishinga connection oi electrical conductivity between m'ron a. POWERS.

CERTIFICATE or CORRECTION HILTON A, PQWERS.

liay ,5, 19 s It'is hereby certified that error appears in the printedspecification of the above nmabered patent requiring: correction asfollows: 'Page 6, first co'lm nn, 1ine' 8, claim 5; [after "through"insert-the words and. semi-colon said a pertm-enand that the said.lietisers Patent should be read with this the: Patent Office correctionthsreinftliat "the same conform to the record of'the case in' Signed andsealed; thisnlhth an or June, A. 1 1 938.

Henry Van-Arsdale', Acting dom'miss'ionerf of Patents.

dum body having refractory insulating material disseminated therethroughand carried by said supporting means.

5. In a liquid iuel apparatusin subcombination,

an aperturedhearth having an upper surface whichis subjected to the heatof the burning fuel; an electrode for igniting said fuel extendingthrough said electrode comprising inner and outer concentric insulatingmembers and means, located below the upper suriace of said hearth,

for holding said outer member in position in and against verticaldisplacement with respect to said 8. The apparatus described in claim 7,wherein said means is operable to allow said conductor and insulator toautomatically undergo relative longitudinal movement in response totemperature variations.

9. The combination with a combustion chamber having a metal combustionring, of an elec- .trical ignition system having two pairs oielectrodes, one electrode oi. each pair being electrically insulatedfrom said ring and the other being electrically connected therewith andthe insulated electrodes being connected to opposite sides of a commonsource of electricity, whereby said ring serves as a part oi theeIectriecircuit for the two pairs of electrodes.

10. An ignition system for oil burners having a hearth and metallicflame ring consisting of a source oi electrical energy, electrodessupported by the hearth and projecting therethrough, second electrodesattached to and-embedded in the metal flame ring adjacent the firstmentioned electrodes thereby forming a spark gap therebetween, saidelectrodes being connected in series with said metal flame ring.

11. An oil burner equippedr with a metal flame ring, a hearth, andelectrical ignition means wherein at least a portion of said metal flamering forms a part of the electrical circuit, said electrical ignitionmeans comprising electrodes projecting through said hearth andcomplementary electrodes therebetween embedded in said metal flame ringadjacent said projecting electrodes to form spark gapswith respectthereto.

12. In a liquid fuel burning apparatus, an ignition'system including awall of thin metal of high heat resistance'and of good electricalconductivity, an electrode comprising a block of material of higherelectrical resistance than said' wall, thin metal supporting meansintegral with said wall to position said block of material, and

a second electrode disposed adjacent said block to form therewith aspark gap.

18. In the apparatus deiined in clair'n 12, said wall having a portioncurved to form a concave fuel impingement face, said curved portionhaving an aperture, said block fitting said aperture and extendingtherebeyond in a direction to the rear of said lace, and said metalsupporting 1 means likewise projecting rearwardly from the edge of saidaperture.

14. In a liquid fuel burning apparatus, anelongated iuel impingementmetal ring carrying a pair of spaced electrodes and itself establishinga connection oi electrical conductivity between m'ron a. POWERS.

CERTIFICATE or CORRECTION HILTON A, PQWERS.

liay ,5, 19 s It'is hereby certified that error appears in the printedspecification of the above nmabered patent requiring: correction asfollows: 'Page 6, first co'lm nn, 1ine' 8, claim 5; [after "through"insert-the words and. semi-colon said a pertm-enand that the said.lietisers Patent should be read with this the: Patent Office correctionthsreinftliat "the same conform to the record of'the case in' Signed andsealed; thisnlhth an or June, A. 1 1 938.

Henry Van-Arsdale', Acting dom'miss'ionerf of Patents.

